After upgrading an Ubuntu installation to 13.10, for some users certain keyboard shortcuts did not work as expected in gnome-shell (version 3.8). The keyboard shortcuts were configured to their default behavior before and did work for some users but not for all users on the system. In particular, the Alt + Tab combination and Caps Lock were affected.

Alt + Tab: Switch Applications vs. Switch Windows

The most annoying misbehavior let Alt + Tab switch to only one different application. It would not cycle through all open applications but stop on the first one. To fix this, I had to open

Settings -> Keyboard -> Shortcuts -> Navigation

and assign the Alt + Tab shortcut to Switch applications. In my case, it was assigned to Switch windows before.

Caps Lock: Incorrectly behaves as backspace

With another user, I observed that the Caps Lock key does not work as Caps Lock key, e.g. as permanent shift key. Instead, it worked as backspace key. For fixing this one, I installed gnome-tweak-tool

sudo aptitude install gnome-tweak-tool

started it and changed to the Typing tab. There, you will find a configuration key for Caps Lock key behavior that I set to Disabled, that wasconfigured to Map Caps Lock an Additional Backspace.

While I have no idea why the Alt + Tab key kombination stopped working after upgrading to Ubuntu 13.10, it might well be that I accidently messed up the Caps Lock settings.